1. Field of the Invention
The present invention relates to processes for iodinating aromatic compounds over non-acid catalysts wherein the activity of the catalysts at low temperatures is enhanced by the presence of an oxidation catalyst.
2. Discussion of Background
It has long been desired to be able to derivatize aromatic compounds and in particular condensed ring aromatic compounds in commercially attractive quantities since many of these compounds possess properties which would fill long sought needs. In particular, the compound 2,6-naphthalene dicarboxylic acid or its esters is particularly desired for use in the manufacture of polyesters which would have excellent barrier properties when fabricated into films, bottles or coatings. However, known techniques for producing 2,6-naphthalene dicarboxylic acid and esters are very expensive and impractical for commercial exploitation.
Synthesis of iodobenzene starting from benzene and iodine is usually carried out in the liquid phase in the presence of an oxidative agent, preferably nitric acid. Such techniques have been described in the literature and in particular in Japanese No. 58/77830, U.S.S.R. Pat. No. 453392 and by Datta and Chatterjee in the Journal of the American Chemical Society, 39, 437 (1917). Other oxidative agents have also been suggested but none of these have proven to be more efficient or convenient than nitric acid. Typical of the other oxidative agents which have been suggested are iodic acid, sulfur trioxide and hydrogen peroxide as described by Butler in the Journal of Chemical Education, 48, 508 (1971). The use of metal halogenides to catalyze iodination has been suggested by Uemura, Noe, and Okano in the Bulletin of Chemical Society of Japan, 47, 147 (1974). The concept of direct iodination of benzene in the gas phase over the zeolite 13X has been suggested in Japanese Patent Publication No. 82/77631 in the absence of any oxidizing agent.
Ishida and Chono in Japanese Kokai No. 59/219241 have suggested a technique for oxyiodinating benzene over very acidic zeolite catalysts having a silica to alumina (SiO.sub.2 :Al.sub.2 O.sub.3) ratio of greater than 10. In this technique benzene is reacted with iodine in the presence of oxygen to produce iodinated benzene. According to this disclosure approximately 96% of the benzene which is converted to the iodinated form. However, the remaining benzene is oxidized to carbon dioxide and other combustion products resulting in the loss of valuable starting material.
Paparatto and Saetti disclosed in European Patent Applications Nos. 181,790 and 183,579 techniques for oxyiodination of benzene over zeolite catalysts. European Patent Application No. 181,790 suggests the use of ZSM-5 and ZSM-11 type zeolites which have been exchanged prior to use with the least one bivalent or trivalent cation. According to this disclosure the utilization of these zeolites in the acid or alkaline form results in a rapid decrease in catalytic activity in relatively few hours.
European Patent Application No. 183,579 suggests the utilization of X type or Y type of zeolite in non-acid form. According to 183,579 the X or Y zeolites have to be used in the form exchanged with monovalent, bivalent or trivalent cations and in particular with alkaline or rare earth cations. The techniques of 181,790 and 183,579 prepare the monoiodobenzene in selectivities in excess of 90% and only distinctly minor amounts of the diiodobenzene compounds.
Accordingly, a need exists for a process which can iodinate benzene at high conversions with substantially no oxidation of the benzene ring.
Further need exists for a process which selectively produces para-diiodobenzene with substantially no oxidation of the benzene ring.
Another need exists for a process which iodinates naphthalene preferentially at the 2-position with minimum formation of oxidation products.
A further need exists for a process which selectively produces 2,6-diiodonaphthalene with minimal oxidation of the naphthalene starting material.